A block copolymer is disclosed, which comprises a first block comprising polymerized units of an alkylene oxide and a second block comprising polymerized units of an alkylene oxide and a lactone, said copolymer being obtainable by polymerizing an alkylene oxide in the presence of an organic initiator to form said first block, and reacting the first block with a mixture of an alkylene oxide and a lactone. Such copolymers are found to have improved foam inhibition characteristics while maintaining their biodegradable properties.